The association between marital quality and diabetes mellitus: A systematic review

Abstract Background and Aims Marital relationship and its quality are among the major psychological factors affecting the multiple aspects of a person's health status. Chronic diseases are also among the factors that affect various aspects of the lives of millions of people including their marital quality status. One of the most important underlying chronic diseases is diabetes. Since the correlation between diabetes mellitus and marital quality has been neglected, this systematic review, as the first one, aims to investigate the association between marital quality and diabetes mellitus. Methods A comprehensive search was conducted among three databases (Medline, Scopus, and Web of Science) until September 2021, which resulted in 189 articles. After assessing the studies based on the inclusion criteria, 14 studies were included. Results The included studies were divided into two general groups. The first group consisted of 3 articles examining the effect of factors related to diabetes on marital quality, and the second group included 11 articles studying the effect of marital quality on diabetes and its factors. In general, the articles investigating the impact of diabetes‐related factors on marital quality showed that diabetes has negative impacts on levels of marital quality. Also, the articles investigating the impact of marital quality on diabetes‐related factors, showed that higher marital quality is associated with a lower risk of developing diabetes, a better quality of life in patients with diabetes, and better adherence to diabetes care regimen. The results regarding diabetes management were conflicting. Gender was mentioned as an important modulator in some of the investigated relationships. Conclusion Marital quality remarkably influences diabetes‐related factors and is itself affected by the condition resulting from diabetes in individuals with diabetes mellitus. However, further studies are required due to the limited number of studies investigating this correlation.


| INTRODUCTION
Marital relationship and its quality are among the major psychological factors that affect the multiple aspects of a person's health status.
Marital quality is defined as a way of determining the overall quality of marriage by several positive and negative characteristics. 1 There are numerous questionnaires designed for the measurement of marital quality such as the Dyadic Adjustment Scale (DAS), which is the most widely used in the studies. 2 Furthermore, marital quality is investigated based on its multiple aspects including positive dimensions 3 like marital satisfaction, adjustment, intimacy, positive supportive interaction, marital support, constructive communication, and enjoyment as well as negative dimensions such as marital stress, marital risk, marital tension, marital strain, and negative unsupportive interactions. The marital relationship quality is considered an important factor related to the quality of life which affects various aspects of health. Some studies have shown that marital quality is directly related to physical health. 4 One of the important factors that should be considered about psychological factors is their relationship and association with chronic diseases. Diabetes is considered a significant global health challenge due to lifestyle changes in recent years. According to a comprehensive report, the Global prevalence of diabetes mellitus was approximately 4.4% (415 million people) in 2015 and it is predicted to reach 10.8% or 642 million people by 2040. 5 Considering the alarming prevalence of diabetes mellitus, this disease has attracted the attention of many researchers in this field. 6 Diabetes mellitus, as a metabolic disease, is identified by hyperglycemia which can cause damage to different organs and may result in several complications. Regarding the characteristics of the disease, diabetes mellitus can be categorized into different types, including type 1 and type 2 diabetes. 7 Diabetes mellitus may lead to other health-related outcomes, including adverse effects on psychological factors such as the increase in depression among patients with diabetes. 8 As mentioned, psychological factors are among the variables that affect different aspects of people's lives. 1 In society, one of the groups that must always keep their lives under severe control to maintain their health is people with chronic diseases. [9][10][11] Diabetes, as one of the most common chronic diseases, 5 has profound effects on different dimensions of people's lives. 8,12,13 In people with chronic diseases such as diabetes, it is important to know the factors that can affect their quality of life and help them manage their disease better.
Marital quality, as well as the relationship between partners, is a factor that most people face in their lives. Therefore, its impact on people's life is undeniable. 4 In this situation, it is necessary to investigate the impact of marital quality on various dimensions related to diabetes. Also, due to the conditions it imposes on a person's life, diabetes can affect the marital quality of people, [13][14][15] and during this process, diabetes may affect itself recursively. In this situation, it is necessary to investigate the mutual impact of marital quality and diabetes, so that related risk factors can be identified and the possibility of effective interventions to improve the quality of life of people with diabetes can be provided.
The influences of diabetes mellitus on the quality of the marital relationship are discussed by several studies. [13][14][15] However, this relationship has been overlooked by researchers and should be investigated in more studies. Also, marital quality can have major effects on various diabetes-related factors, such as disease development, diabetes management, quality of life, and adherence to diabetes care regimen. [16][17][18][19][20][21][22][23][24][25][26] In a situation where this issue has never been systematically investigated, new studies in this field are designed and implemented without a strong background, and therefore it is not possible to make the most of the potential of the obtained results. In this situation, this study, as the first systematic review to investigate the association between marital quality and diabetes mellitus, aims to become a guide for future studies to choose their objectives more accurately.

| Inclusion/exclusion criteria
The articles were included according to these criteria: (1) the studies investigating the relationship between marital quality and diabetes mellitus; (2) the article was published in English The exclusion criteria were as follows: (1) studies discussing the relationship between marital quality and other factors in patients with diabetes which were not related to the disease (2) reviews, letters, conference papers, and editorials Authors (M. R. and E. J.) independently searched the databases and screened the title and abstracts of the articles based on the inclusion/exclusion criteria. After the first screening, potentially eligible articles were screened by two reviewers (M. R. and E. J.) based on reviewing the full text according to inclusion/exclusion criteria. The mentioned steps were performed while the two authors were blinded to each other. The disagreements on articles were resolved by discussion between authors. After performing the above steps and according to the inclusion/exclusion criteria, 14 studies were included in this systematic review. Figure 1 illustrates the diagram of the literature search.

| Risk of bias assessment
We used the Newcastle-Ottawa scale 27 to evaluate the cohort studies. This scale consists of three groups: selection, comparability, and outcome. A cohort study can get a maximum of 1 score for each question of selection and outcome, and a maximum of 2 scores for comparability. Thus, a study can get a maximum of 9 scores from the Newcastle-Ottawa scale. Table 1 shows the result of the qualitative analysis of cohort studies.
Also, an adapted version of this scale was used for evaluating cross-sectional studies which include three groups of selection (maximum of 5 scores), comparability (maximum of 2 scores), and outcome (maximum of 3 scores). Table 2

| Data extraction
The required data were extracted by two independent researchers and the findings were reported based on PRISMA. 28

| RESULTS
The preliminary search of three databases resulted in 189 articles. The first group consisted of 3 articles 13-15 examining the influence of diabetes mellitus factors on the level of marital quality, and the second group included 11 articles 16-26 studying the impact of marital quality status on diabetes-related factors. In the following, we will first present the studies of the first group, and then the studies related to the second group will be presented. Table 3 summarizes the characteristics and significant results of included studies.

| Impact of diabetes-related factors on marital quality
The studies in this section fall into two categories. Whereas, there was no relationship between marital quality and adherence to blood glucose testing and control. Also, the initial level of marital quality was not a predictor of adherence to different aspects of diabetes self-care at the end of the study. 24  The other cross-sectional study did not indicate the same results stated by the previous article and showed the significant effect of type 2 diabetes on marital satisfaction. 15 Despite studying the relationship only in the female group, its results are more noteworthy since it has studied both patients with diabetes mellitus type 1 and 2.
A cross-sectional study examined a different aspect of diabetes and stated the benefits of beliefs about diabetes on marital quality. 14  Nevertheless, some contradictory results on this association, especially in men, need to be clarified in future research.
Diabetes mellitus requires lifelong management to prevent other complications of this metabolic disease such as neuropathy and nephropathy. 36 Numerous studies examined the effect of marital relationship quality on diabetes management, and their consensus was on the positive association between these factors. 17,18,20,21,23 Fisher et al. showed a direct link between relationship quality and diabetes management. 17 This study has some biases including a 47% acceptance rate that shows losing about half of the study sample.
Also, the study by Liu et al. 18 requires more investigation due to its challenging results of the direct association between negative marital quality and diabetes management in men. The other cross-sectional study by Naqvi et al. 20 investigated the role of sex, race, and relationship quality in diabetes-related self-care and self-efficacy.
Considering the role of age and gender in this association may make its results more worthwhile. The other study investigating the association between different aspects of marital quality and diabetes management was by Roberson et al. 21 As stated previously, its results were more noteworthy, since they included different socioeconomic factors in their analyses. The prospective cohort study over 1 year by Trief et al. 23 16 showed the association between marital quality and diabetic compatibility and its different aspects based on gender. But its RASTKAR and JALALIFAR spousal/partner quality. The negative associations between stress and blood pressure were observed specifically among the individuals reporting less reliance, more confiding, and greater demands from their spouses/partners. 40 Therefore, as can be seen, marital quality has significant effects on chronic diseases.
Finally, to summarize the results of this study, the following section is given: The studies were divided into two general groups.

| LIMITATION
This study had serious limitations. The most important limitation is the lack of related articles. Unfortunately, the role of psychological factors, especially marital quality, in chronic diseases and vice versa has been neglected for many years, and there is no suitable comprehensive keyword for marital quality. In the results section, the studies are classified into six sub-titles, each of which can be the subject of an article. But we believed that detailing the topic of this article and making it more precise, although it would make the study more specialized, due to the general neglect of this relationship by researchers, could not be a proper guide for subsequent studies. Also, by narrowing the topic, the number of articles (which is still few) would be significantly reduced and their results would not be suitable for independent presentation. In this situation, the present study tried to investigate the relationship between diabetes and marital quality in a broad way to prepare the ground for further studies in this field in a more targeted and detailed manner. The current systematic review tries to provide a general summary of the studies conducted in the past 30 years and guide the new studies under the six sub-titles introduced.
It is natural that due to the small number of studies, the results presented in each of the subtitles are not strong enough, especially since the studies themselves had serious limitations that were presented in the discussion section. Also, some articles could be presented in more than one subtitle.
In addition, owing to the limitation of studies, variation in data collection, methods of marital quality measurement, and studied population, conducting a meta-analysis was not possible. Future studies can provide the opportunity of conducting meta-analysis and more accurate and reliable conclusions by using the results of this systematic review and not repeating the biases raised for the included studies in the discussion section.